Transannular Hydrogen Transfer in the Steroid Series¹

Mechanisms Of Epoxide Reactions

“…Other recent examples of diaxial opening of steroid epoxides include the reactions of 2a,3a-epoxides with lithium aluminum hydride (40), lithium and ethylamine (99), and sulfuric acid in aqueous acetone (239), of 2P ,SP-epoxides with sulfuric acid in aqueous acetone (239), of 4a,5a-and 40,5p-epoxides with lithium aluminum hydride (35), of 5a, 6a-epoxides with methylmagnesium iodide (41), lithium and ethylamine (99), and lithium aluminum hydride (207), of 5p,6/3-epoxides with lithium and ethylamine (99) and lithium aluminum hydride (207), of 7a,8a-and Sa,lla-epoxides with lithium and ethylamine (99), of 9p, llp-epoxides with hydrogen fluoride (70) and hydrochloric acid (283), and of 16a, 17a-epoxides with hydrochloric acid (71) and hydrobromic acid (223).…”

“…a 9p, llp-epoxide with aqueous perchloric acid (282,283). The mechanism suggested involves migration of H-from C w to C m , with subsequent loss of a proton from Cg:…”

Biogenetic-Type Rearrangements of Terpenes

“…Exposure of either sativene (193) or copacamphene (202) to cupric acetate in refluxing acetic acid produces the same equilibrium mixture of sativene (7-8%), cyclosativene (194, 32%), and isosativene (204, 60-61 %) (278,279). The greater thermodynamic stability of sativene over copacamphene is a consequence of the axial configuration of the isopropyl group on the six-membered ring of the latter.…”

“…A case of 1 ,3-hydrogen rearrangement was discovered in the reaction of steroidal epoxide 133 with 60% perchloric acid in chloroform (202). The fact that the .1.…”

“…lt is interesting to note that diol (199) is a natural product and is formed in the ringopening of IX-copaene epoxide (198) with net inversion at the tertiary center (274 The Wagner-Meerwein rearrangement of copabornanes and ylangobornanes to copacamphanes and sativanes has been observed. Thus, copabornyl brosylate (190-0Bs) undergoes rearrangement and proton elimination to copacamphene (202) (277). In a similar fashion sativene (193) is formed from isoylangobornyl mesylate (203) (116,117).…”